The present invention relates to a method for producing a novel thermoplastic resin composition which has improved mechanical properties, especially improved impact resistance and which can be utilized for making shaped articles, sheets or films by injection molding or extrusion molding.
Generally, saturated polyester resins are superior in weather resistance, electric characteristics, chemical resistance, wear resistance and thermal aging resistance and are widely used as engineering plastics. However, they have difficulties in impact resistance which hinder development for practical use thereof.
Hitherto, there have been proposed various methods for improving impact resistance of saturated polyester resins.
Representatives thereof are, for example, as follows: a method of adding ethylene copolymer containing an active group reactive with saturated polyester resin as well as having rubber elasticity; a method of melt mixing with an .alpha.-olefin-glycidyl methacrylate copolymer; and a method of adding a polyfunctional compound selected from the group consisting of epoxy compounds, isocyanate compounds and carboxylic acid anhydrides or a carboxylic acid to an olefinic copolymer comprising .alpha.-olefin and a glycidyl ester of .alpha., .beta.unsaturated acid. These methods are disclosed, for example, in Japanese Patent Examined Publication (Kokoku) Nos. 28223/84 and 47419/83 and Japanese Patent Unexamined Publication (Kokai) Nos.137154/80 and 159247/81.
However, it has been found that these conventional methods can afford molded articles which are improved in impact resistance to some extent, but these are not satisfactory yet. The articles are not satisfactory in balance of stiffness and impact resistance, either.
That is, the somewhat improved impact resistance and flexibility are offset by the mechanical properties such as stiffness, tensile strength and hardness which are considerably inferior to those of saturated polyester per se.
Therefore, it is important to accomplish a method for making a composition free from the above problems by blending a ethylene copolymer with saturated polyester resins and the development therefor has been earnestly demanded.